Wednesday, August 30, 2017

A Brief History of Harvey

"Local rainfall amounts of 50 inches would exceed any previous Texas rainfall record. The breadth and intensity of this rainfall are beyond anything experienced before. Catastrophic flooding is now underway and expected to continue for days."
 NWS Weather Prediction Center, Sunday, August 27

Harvey started out as a rather innocuous disturbance in the Caribbean more than 10 days ago. It was disorganized and at times looked like it was going to fall apart. On Thursday, August 17 the disturbance was promoted to Tropical Storm Harvey. By late on Saturday August 19 Harvey had weakened into a tropical wave. There were no advisories issued Sunday through Tuesday as what was left of Harvey drifted west. On Wednesday, August 23  a Hurricane Hunter found that Harvey had regenerated in the Bay of Campeche, and advisories were issued. At that time Harvey was expected to make landfall along the southern Texas coast by Saturday morning. It was also expected that Harvey might slow down or stall out over southeast Texas,

Harvey intensified quickly on Thursday morning and was forecast to become a hurricane before landfall. By early afternoon on Thursday the storm had become Hurricane Harvey, with further intensification expected. By midnight Harvey was a Category 2 storm with winds near 100 mph. In the 4:00 a.m. advisory on Friday the National Hurricane Center expected further intensification and expected Harvey wander slowly through southeast Texas for the next five days. It also included this statement:

"Devastating and life-threatening flooding is expected across the middle and upper Texas coast from heavy rainfall of 15 to 25 inches, with isolated amounts as high as 35 inches, from today through next
Wednesday."


The 4:00 p.m. advisory on Friday indicated Harvey's winds had increased to 125 mph, and by 7:00 p.m. Harvey was a category 4 storm with winds of 130 mph. Hurricane Harvey made landfall just before 10:00 p.m. CDT on the Texas coast over the northern end of San Jose Island about 4 miles east of Rockport. The storm stalled about 60 miles east of San Antonio for awhile, then gradually drifted southeast back into the Gulf of Mexico. Early this morning (August 30), Harvey made landfall for a second time just west of Cameron, Louisiana. The excellent graphic below shows Harvey's travel from the Atlantic to this morning's second landfall.

The path of Hurricane Harvey.
Credit: Brandon Moses (via Twitter)

Josh Morgerman (@iCyclone), a hurricane chaser, was in Rockport, TX when Harvey made landfall. You can read his interesting account of his "chase" of Harvey at this link.

 Initially the high winds and storm surge were the focus of attention. The Texas coast from Rockport to Port Aransas was raked by 100+ mph winds, and storm surge quickly flooded coastal areas. As Harvey drifted inland the winds weakened, but the worst of the storm was starting to take shape.

This is the  storm relative velocity image (SRV) out of Corpus Christi radar at 4:10 p.m. CDT on Friday, August 25. Max winds outbound ~140 mph (brown), inbound ~115 mph (blue).


With a few exceptions (Hurricane Andrew, for one) winds usually aren't the worst of a hurricane or tropical storm. Torrential rain and resultant flooding (as well as flooding from storm surge) usually result in the most damage. As Harvey moved ashore late on Friday feeder rain bands on the east side of the storm were starting what was to be an epic and unprecedented tropical rain event. The astounding forecasts of up to 50 inches of rain verified by Tuesday afternoon. Though the rain ended in Houston, it was unrelenting in eastern Texas and western Louisiana. 26 inches of rain fell in 24 hours in Beaumont, TX, and radar estimated rainfall as of early afternoon today was in excess of 50 inches there as well.

Radar estimated rainfall from the Lake Charles, LA radar at 10:50 a.m. CDT Wednesday, August 30. Rain continued for several hours after this image. Max value indicated by radar was 50.80". The white to gray shading is 40 to 50 inches.
Tonight Harvey was downgraded to a tropical depression. The storm is expected to continue moving northeast and into Ohio by Saturday.producing heavy rain in the Tennessee and Ohio Valleys and south.


Next post: CoCoRaHS Observers, Rainfall, and Hurricane Harvey

3 comments:

  1. Nice description of the events. It makes it clear that calling an evacuation in Houston would have been the wrong thing to do; by the time it was clear the storm would be really bad, there would not have been time to get millions out of town and any attempt at a mass evacuation would have resulted in many deaths for those trapped on roads by rapid flooding.

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  2. Thank you - this is so helpful to understand the development of this storm.

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  3. Thanks Steve for this great documentation of historic Harvey.

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